I decided to use a VCR since they are practically junk these days and can be easily obtained from a Good Will for 5 bucks; much cheaper than hard drives DVR systems. A single VHS tape could last 6 hours in record time. To stretch this maximum record time even further I made the system only record a short period once it detected motion.
I imagined a circuit that upon detecting motion would automatically press record, wait a period (say a minute) then press pause or stop. To implement motion detection I re-purposed my Harbor Freight driveway detection system which is pretty much a PIR motion detector that transmits a radio signal to a receiver which sounds a bell during motion. The motion sensor would act as normal but an activation signal would be taken from the receiver that would manipulate the VCR.
I was given a broken digital camera which turned on but did not take pictures, luckily the CCD capture device still worked along with its video out capabilities. This easily converts into a CCTV camera by plugging in a power adapter, the video out cable, and turning off the auto-off feature. I took it apart to take out the IR filter for night vision capability.
All that was needed for this system to work was a circuit which accepted a trigger signal from the motion sensing system and outputted to the VCR to record and after a certain period of time pause. My design criteria for the circuit functionality was simple.
I saw this as a fun design challenge to brush up on my electronics skills. I came up with a circuit designing as far as I could without referring to any books or online tutorials.
After much testing, the entire system was humming. It took much more work than I anticipated. The circuit was redesigned about 4 times to get it just right. The radio signal between the motion sensor and the receiver (installed inside the VCR) interfered with the video signal so large bypass capacitors were added to DC source lines to filter noise.
The RC timer was set fixed at 60 seconds, in the future, I may make this timer adjustable with a knob but it seems fine for now. Unfortunately the latency between the detected motion and when the VCR actually begins to record is about a 1 to 2 seconds. Not good for recording high speed targets. This is due to the mechanical spin up time the VCR needs after the record button is actuated.
The total money spent was around $20. The VCR being $5, op-amp chip and circuit stuff around $2, and the driveway detection system about $14 (even cheaper with coupon at Harbor Freight). I suppose one could use just a motion sensor device to bring the price down even cheaper. The nice thing about the driveway sensor is that it can be placed away from the camera and remotely signal the circuit within the VCR. For predictable targets, one could then strategically place the sensor in order to compensate for the 1 to 2 second delay the VCR requires to start recording.